The invention concerns a fuel tank and more particularly a fuel tank suitable for a motor vehicle.
A typical form of fuel tank, for example for a motor vehicle, includes means for delivering the fuel tank from the internal volume of the tank to the engine, and means for the introduction of air into and the venting of air from the tank. The tank further includes a filler pipe which is closable at the intake end and which, in the region of its mouth opening into the interior of the tank, that is to say at the outlet end of the filler pipe, is provided with at least one first valve which is operable to sealingly close off at least when there is a surge of fuel back into the filler pipe, which will be referred to as fuel blowback.
Modern fuel tanks and fuel delivery systems in particular for motor vehicles are being subjected to ever increasing demands in terms of sealing integrity thereof. On the one hand, continuous hydrocarbon emissions arising due to diffusion or very minor leakage are to be avoided, while on the other hand both when filling the motor vehicle tank and also in the event for example of an accident, the aim is to guarantee that liquid or gaseous hydrocarbons cannot escape from the tank. For example in the event of the motor vehicle in which the tank is fitted turning over, or in the event of the tank filler pipe being torn away as a result of impact, it is still necessary to ensure that the fuel tank is still sealingly closed off. Not least, at the end of a tank filling procedure, it is also necessary to ensure that no fuel can splash or slop back out of the tank. It will be noted that, when a tank is being filled with a refuelling nozzle, up to 60 liters of fuel per minute can be fed to the fuel tank, depending on the design configuration of the refuelling pump, so that, depending on the configuration of the filler pipe involved, it would be possible, without special measures being taken, for fuel to suffer a surge back in the filler pipe, particularly when the fuel is diesel fuel which has a severe tendency to foam up.
For that reason the outlet end of the filler pipe of a fuel tank has been provided with a check or non-return valve or check flap member, operable for sealingly closing off the fuel tank, in other words, the check valve is only opened in a motor vehicle tank filling procedure, by virtue of the fuel flowing into the tank.
Finally, it is known for the sealing integrity of the fuel tank to be continuously checked during operation of the motor vehicle and for any lack of sealing integrity to be displayed, for example by means of an on-board computer. Such OBD-functions (on-board diagnosis) also include for example checking whether the fuel cap has been fitted to the tank and/or locked. Sealing integrity of a fuel tank is usually checked by subjecting the tank to a reduced pressure therein. When check valves which close with a sealing action are used in the filler pipe of the fuel tank, such a sealing integrity checking operation can only be carried out for the main volume of the fuel tank, without involving complicated and expensive by-pass lines, but it cannot also be implemented in respect of the filler pipe, which however would be desirable. A further disadvantage of such an arrangement is that an emergency valve for venting the tank in the event of an unacceptable increase in pressure occurring therein, for example due to the severe action of heat thereon, cannot be implemented by way of the fuel cap or cover closure of the filler pipe. It is therefore necessary for such a valve to be provided in the actual wall of the fuel tank, but that entails the disadvantage that this can increase the fuel tank emission values. Furthermore that will also increase the fuel tank manufacturing cost.
An object of the present invention is to provide a fuel tank for example for a motor vehicle, which can avoid the disadvantages referred to herein before.
Another object of the present invention is to provide a motor vehicle fuel tank so designed as to permit the implementation of a checking procedure for sealing integrity of a filler pipe of the tank as well as emergency venting of the tank, using a structurally simple tank configuration.
In accordance with the principles of the present invention the foregoing and other objects are attained by a fuel tank, as for a motor vehicle, comprising means for delivering fuel from the tank to an engine, and means for the introduction of air into and the venting of air from the tank. The fuel tank has a filler pipe which is closable at its intake end and which in the region of the mouth opening thereof into the interior of the tank, at the outlet end of the filler pipe, includes at least one first valve which sealingly closes off at least in the event of a fuel blowback. The fuel tank further includes at least one second valve which is disposed in the filler pipe in the region of the outlet end thereof, wherein the first valve can be bridged over by the second valve.
As will be apparent from the description hereinafter of a preferred embodiment of the invention a fuel tank in accordance with the present invention means that it is possible to run a check on the sealing integrity of the filler pipe and also to carry out emergency venting of the fuel tank, using structural means which are comparatively simple. There is also no need to lay relatively long by-pass conduits nor is there any requirement for one or more valves to be additionally disposed in the wall of the tank.
In accordance with a preferred feature of the invention the second valve is in the form of a valve which is operable to open and close in the same direction with the first valve and which is adapted upon actuation to respond to a lower actuating force than the second valve. In that way, the second valve opens when the fuel tank is subjected to a reduced pressure therewithin in the usual fashion, whereby a measuring procedure involving the production of a reduced pressure within the tank for testing, same can also involve the region of the filler pipe, without the sealing integrity of the system generally being adversely affected.
In a further preferred feature the second valve can be disposed in a valve body of the first valve. That can advantageously combine a number of functionalities in one structural unit, occupying a small amount of space.
A further preferred feature provides that the first valve is in the form of a spring-loaded non-return or check valve.
The second valve can be in the form of a resilient disk or plate member which when not actuated closes at least one passage in the valve body of the first valve. That can close the passage or passages, with a comparatively small amount of force, as it is to be assumed in any case that there is an increased pressure in the interior of the fuel tank, in the operative condition.
In a preferred feature of the invention, the second valve can be so designed for example that it is openable at a differential pressure with a fall to the interior of the tank of between about 5 and 20 mbars. Usually, in a procedure for checking the sealing integrity of a fuel tank by means of producing a reduced pressure therein, differential pressures of about 25 mbars are involved. It is at any event necessary to ensure that the second valve opens at a differential pressure value markedly below the testing differential pressure.
In an alternative configuration of the valve in accordance with the invention the second valve can be in the form of a safety valve which opens and closes in the opposite direction to the first valve.
The second valve can be for example in the form of a spring-loaded valve, while the second valve may have a valve body which is in the form of a sealing seat for the valve body of the first valve.
Preferably, the valve bodies of the first and second valves are arranged in a common valve housing whereby the valve arrangement according to the invention is particularly compact.
Preferably, the valve body of the second valve can be of an annular configuration and in the closed condition seals off an annular space or bypass between the valve body of the first valve and the valve housing. The valve body of the first valve can at least in the closure position engage into or pass through the valve body of the second valve.
In accordance with another preferred feature of the invention the second valve is in the form of a valve which is operable to open and close in the same direction as the first valve and which is adapted upon actuation to respond to a lower actuating force than the first valve, and further including a third valve in the form of a safety valve which is operable to open and close in opposite relationship to the first valve. In this embodiment of the invention, a total of three valve functions or three switching paths can be embodied in a common valve housing.
Further objects, features and advantages of the invention will be apparent from the description hereinafter of a preferred embodiment thereof.